Silversides, continued 



Menidia species has been noted (Lee et al. 1980, 

 Bengtson 1984, Bengtson 1985). 



Food Items : Various larval and adult crustaceans are 

 the predominant food items of Menidia (Odum 1971, 

 Levine 1980). Silversides less than 16 mm SL feed 

 primarily on the larval stages of copepods and other 

 crustaceans (Odum 1971). Larval M. beryllina have 

 been successfully reared on/4rtem/anauplii, nutrition- 

 ally similar to known natural foods such as the copepod 

 Acartia (Bengtson 1985). Juveniles 15 to 42 mm SL 

 are known to feed on mollusc veliger larvae. Detritus 

 is a major item in small size classes, but is fairly 

 common in larger ones as well, although declining in 

 importance (Darnell 1958, Ruebsamen 1972, Carrand 

 Adams 1 973, Diener et al. 1 974). Detritus is probably 

 obtained as suspended material rather than from the 

 benthos (Carr and Adams 1 973). Isopods and amphi- 

 pods form the bulk of food in all size classes with 

 isopods and veligers declining in fish larger than 40 to 

 54 mm TL to be replaced by insects, especially chi- 

 ronomid larvae, pupae and adults (Darnell 1 958, Levine 

 1980). Larger fish also consume more megalops 

 larvae, copepods, and mysids than smaller size classes 

 (Carr and Adams 1 973). Schizopods are consumed by 

 all size classes, but mainly by intermediate size fish. 

 Fish form a small but significant diet item (Levine 

 1 980). Fish prey include bay anchovy, gulf menhaden, 

 silversides, and gulf pipefish (Syngnathus scovelll). 

 Miscellaneous items consumed include sand, filamen- 

 tous algae, vascular plant material, rotifers, annelids, 

 ostracods, arachnids, eggs, cysts, and fish remains 

 (Darnell 1958, Ruebsamen 1972, Levine 1980). 



Biological Interactions 



Predation : Silversides are important forage fishes for 

 many commercial and recreational fishes and othertop 

 trophic level carnivores (Simmons 1957, Garwood 

 1968, Hubbs 1982). Reported predators include gar 

 (Lep/sosfeL/sspecies), catfish (/cfa/urusspecies), hard- 

 head catfish, silversides, spotted seatrout, red drum, 

 white bass (Morone chrysops), largemouth bass 

 (Micropterus salmoides), and crappie (Pomoxis spe- 

 cies) (Simmons 1957, Darnell 1958, Garwood 1968, 

 Hubbs et al. 1971, Diener et al. 1974, Hubbs 1982, 

 Rozas and Hackney 1984, Wurtsbaugh and Li 1985). 

 Near Santa Rosa Island, Florida, pinfish have -been 

 reported to prey on newly-spawned eggs of M. 

 peninsulae adhering to red algae (Middaugh and Hem- 

 mer 1987a). 



Factors Influencing Populations : Hybridization be- 

 tween Menidia peninsulae and M. menidia has been 

 reported in northeastern Florida (Johnson 1975), and 

 hybridization between M. beryllina and M. peninsulae 

 is known to occur in Texas estuaries (Echelle and 

 Echelle 1 997). The clonal lineages of the/W. clarkhubbsi 



complex may be ephemeral, because of lack of genetic 

 variation and recombination, accumulation of deleteri- 

 ous alleles, and inability to adapt to changing environ- 

 mental conditions (Echelle and Echelle 1997). How- 

 ever, this asexual life history strategy provides a short- 

 term reproductive advantage, and enables utilization 

 of intermediate habitats. Trophic competition and 

 partitioning has been demonstrated between M. 

 menidia and M. beryllina in Rhode Island estuaries. 

 The later spawning time and slower growth rate of M. 

 beryllina may be an adaptation to the lower zooplank- 

 ton abundance later in the season (Bengtson 1984, 

 Bengtson 1985). However, in situ experiments in 

 Rhode Island suggest that the size-specific survival of 

 M. beryllina larvae may depend more on the suite of 

 predators present than on a limited zooplankton forage 

 base (Gleason and Bengtson 1996). The key silver- 

 side (M. conchorum) is being considered as a candi- 

 date species under the federal Endangered Species 

 Act because of its rare status (NMFS 1997, Jordan 

 pers. comm.). 



Personal communications 



Jordan, Terry. NOAA National Marine Fisheries Ser- 

 vice, Silver Spring, MD. 



Ross, Stephen T. University of Southern Mississippi, 

 Hattiesburg, MS. 



References 



Arnold, E.L, Jr., R.S. Wheeler, and K.N. Baxter. 1 960. 

 Observations on fishes and other biota of East Lagoon, 

 Galveston Island. U.S. Fish Wildl. Serv., Spec. Sci. 

 Rep. No. 344, 30 p. 



Bailey, R.M., H.E.Winn, and C.L.Smith. 1954. Fishes 

 from the Escambia River, Alabama and Florida, with 

 ecologic and taxonomic notes. Proc. Acad. Nat. Sci. 

 Phila. 106:109-164. 



Barrett, B.B., J.L. Merrel, T.P. Morrison, M.C. Gillespie, 

 E.J. Ralph, and J.F. Burdon. 1978. A study of 

 Louisiana's major estuaries and adjacent offshore 

 waters. Louis. Dept. Wildl. Fish. Tech. Bull. No. 27, 1 97 

 P- 



Bengtson, D. A. 1984. Resource partitioning by Menidia 

 menidia and Menidia beryllina Mar. Ecol. Prog. Ser. 

 18:21-30. 



Bengtson, D.A. 1985. Laboratory experiments on 

 mechanisms of competition and resource partitioning 

 between Menidia menidia (L.) and Menidia beryllina 

 (Cope) (Osteichthyes: Atherinidae). J. Exp. Mar. Biol. 

 Ecol. 92:1-18. 



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